Lufthansa, Europe’s largest airline by revenues, is considering legal action to head off a four-day strike by its pilots starting at midnight on Sunday. The dispute threatens to escalate into one of the severest industrial conflicts in recent German history.

Stefan Lauer, board member responsible for personnel, said that Lufthansa’s lawyers would report to him by Monday on options for halting the strike, called this week by Vereinigung Cockpit, the pilots’ trade union.

Cockpit has said its main goal is to secure jobs in Germany and has called on more than 4,000 pilots to take part in the strike , which will also affect Lufthansa Cargo and Germanwings, its low-cost carrier.